Serial radio frequency to baseband interface with programmable clock

ABSTRACT

An interface between an RF processing section and a baseband processing section supports general purpose message transmission as well as satellite positioning system signal sample transmission between the RF processing section and the baseband processing section. The interface includes a bi-directional message serial interface and a data serial interface. The complexity of the data serial interface may be minimized by using a single data bit signal line in the data serial interface.

1. CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to U.S. patent application Ser. No.10/369,853 filed on Feb. 19, 2003.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to an interface for coupling a radio frequency(RF) processing section to a baseband processing section. Morespecifically, this invention relates to a serial message and datainterface between an RF processing section and a baseband processingsection.

2. Related Art

The worldwide use of wireless devices such as two-way radios, pagers,portable televisions, personal communication systems (“PCS”), personaldigital assistants (“PDAs”) cellular telephones (also known as “mobilephones”), Bluetooth devices, satellite radio receivers and SatellitePositioning Systems (“SPS”) such as the Global Positioning System(“GPS”), also known as NAVSTAR, is growing at a rapid pace. Currenttrends are calling for the incorporation of SPS services into a broadrange of electronic devices and systems, including PDAs, cellulartelephones, portable computers, automobiles, and the like.

At the same time, manufacturers design their devices using verydifferent architectures, spanning a wide variety of processors,frequency references clock rates, and the like. The manufacturers arealso very interested in keeping costs as low as possible while providingas much functionality (including SPS capability) as possible. Inparticular, architectures which split SPS signal processing between aradio frequency (RF) front end a baseband processing section continue tobe popular.

For example, SiRF Technology, Inc. of San Jose, Calif. made popular anSPS chipset that included the GRF1 RF chip and GSP1/LX basebandprocessing chip. These two devices are described in detail in theSiRFStar® I GPS Architecture GRF1 and GSP1 data sheets. As shown in FIG.1, the RF chip 102 communicated data samples to the baseband chip 104using differential sign signal lines (labeled SIGN), differentialmagnitude signal lines (labeled MAGNITUDE), a GPS clock signal line(labeled GPSCLK), and an acquisition clock signal line (labeled ACQCLK).The baseband chip 104 could communicate with the RF chip 102 in alimited single purpose fashion, namely, by using automatic gain control(AGC) clock, data, and strobe signal lines (labeled AGCCLK, AGCDATA, andAGCSTRB respectively) to provide AGC data to the RF chip 102.

More recent SPS signal processing chipset solutions include theSiRFStar® lie (centered around the GRF2i RF chip and GSP2e basebandchip) and SiRFStar® IIt (centered around the GRF2i RF chip and GSP2tbaseband chip) solutions. Both retained the multiple signal lines usedto communicate data samples from the RF section to the baseband sectionand the unidirectional communication of AGC information from thebaseband section to the RF section. However, the baseband sectioncommunicated AGC information unidirectionally to the RF chip using asingle pulse width modulated output that the RF chip sampled. In otherwords, the SiRFStar® IIe eliminated the multiple signal line AGCcommunication path in favor of a single output line.

Despite the capabilities of previous SPS chipset solutions, most onlyfunction with one or two very specific input frequency references, andalso require several chipset pins (e.g., separate sign and magnitudedata pins) to communicate data signals between the RF section and thebaseband section. As the number of interface signals grows, so does thepin count and manufacturing cost of the chipset. Furthermore, onlysingle purpose unidirectional communication capability has existedbetween the baseband and RF sections. As a result, the pre-existingchipset are limited in their flexibility and sophistication forincorporation into the widest possible range of devices.

Therefore, a need exists for an RF to baseband interface that overcomesthe problems noted above and others previously experienced.

SUMMARY

The invention provides an interface (and methods of operating orproviding interfaces) between an RF processing section and a basebandprocessing section. The interface supports general purposebi-directional message transmission between the RF processing sectionand the baseband processing section. The interface further supportstransmission of SPS signal samples between the two processing sectionswithout adding undue complexity to the interface.

In one embodiment, the interface includes a message serial interface anda data serial interface. The message serial interface communicatesmessages between the RF section and the baseband section. The dataserial interface communicates SPS signal sample data from the RF sectionto the baseband section.

The complexity of the data serial interface may be reduced, for example,by using a single data bit signal line to serially carry signal samplesfrom the RF section to the baseband section. The data serial interfacemay also include a data clock signal line that provides timing for thesignal samples. In particular, as an example, the data clock signal linemay carry a data clock (that includes rising edges and falling edges)nominally running at 16 fo, where fo=1.023 MHz, while the data bitsignal line may carry a data signal comprising serially transmitted databits. In one embodiment, a first type of data bit is valid on the risingedge of the data clock and a second type of data bit is valid on thefalling edge of the data clock. As an example, the first type of databit may be a sign bit, while the second type of data bit may be amagnitude bit.

As noted above, a message serial interface communicates messages betweenthe processing sections. The message serial interface may include amessage-in signal line, a message-out signal line, and a message clocksignal line. In some embodiments, the message serial interface may alsoinclude a slave-select signal line.

Other apparatus, systems, methods, features and advantages of thepresent invention will be or will become apparent to one with skill inthe art upon examination of the following figures and detaileddescription. It is intended that all such additional systems, methods,features and advantages be included within this description, be withinthe scope of the present invention, and be protected by the accompanyingclaims.

BRIEF DESCRIPTION OF THE FIGURES

The components in the figures are not necessarily to scale, emphasisinstead being placed upon illustrating the principles of the invention.In the figures, like reference numerals designate like parts throughoutthe different views.

FIG. 1 shows a prior interface between a GPS RF chip and a basebandchip.

FIG. 2 illustrates a satellite positioning system receiver that includesan RF processing section coupled to a baseband processing section by aninterface that includes a message serial interface and a data serialinterface.

FIG. 3 illustrates a timing diagram that shows the relationship betweena data clock and a data signal carried, respectively, on a data clocksignal line and a data bit signal line that form the data serialinterface shown in FIG. 2.

FIG. 4 illustrates a timing diagram that shows the relationship betweena message clock and message data bits carried, respectively, on amessage clock signal line and message data bit signal line that formpart of the message serial interface shown in FIG. 2.

FIG. 5 shows a method for interfacing an RF processing section and abaseband processing section.

DETAILED DESCRIPTION

A typical satellite positioning system (“SPS”) system has approximately12 satellites that may be visible at any one time to a wireless device.As used in this document, SPS means any system utilizing satellitesand/or land-based communications devices for providing or enabling thedetermination of a location of the wireless device on the earth,including, but not limited to: a global positioning system (“GPS”) (suchas NAVSTAR), GLONASS, LORAN, Shoran, Decca, or TACAN. For the purposesof discussion, specific examples of an interface between a GPS RFprocessing section and a baseband processing section are described.However, the principles underlying the interface are applicable tointerfacing RF processing and baseband processing sections in general.

Turning first to FIG. 2, that figure shows a receiver 200 of a satellitepositioning system. The receiver 200 includes an RF processing section202 coupled to a baseband processing section 204 using an RF-to-basebandinterface 206. The RF processing section 202 receives SPS signals, forexample the 1575.42 MHz GPS signal, on the RF input 207.

The receiver section 200 may be generally regarded as including an RFfront end 224 and a baseband back end 226. The RF front end 224 includesthe RF processing section 202 and RF-to-baseband interface 206. The RFfront end 224 processes the SPS signals received on the RF input 207through a sequence of downconversion, automatic gain control, and analogto digital conversion. The baseband back end 226 includes the basebandprocessing section 204 and RF-to-baseband interface 206. The basebandback end 226 processes (using a microcontroller core, CPU, or othercontrol logic) the sampled data provided by the R front end 224. Thebaseband back end 226 communicates the processed data to a digitaldevice (e.g., a digital signal processor, general purposemicrocontroller or CPU, or host PC) using one or more address, data,control, and clock signals that comprise the digital communicationinterface 222.

Either or both of the RF front end 224 and baseband back end 226 may beimplemented as individual single integrated circuits, for example. Thus,the RF front end 224 may be a single package that includes the RF input207 (e.g., a particular input pin on the package), RF processing section202, and interface 206 (e.g., a set of interface pins as described inmore detail below). Similarly, the baseband back end 226 may be a singlepackage that includes the baseband processing section 204, interface206, and digital interface 222. The processing performed by the RFprocessing section 202 and baseband processing section 204 may be thatset forth in more detail in the SiRFStar® I, II, or III chipset datasheets, while the interface 206 is described in more detail below.

Although, as shown in FIG. 2, the functional division between the RFfront end 224 and the baseband back end 226 lends itself to beingdivided into two separate integrated circuits, many otherimplementations are possible. As one example, numerous discrete logicand signal processing circuit blocks may implement the RF, baseband, andinterface 206 functionality. As additional examples, any of thecircuitry underlying the functionality of the RF front end 224 and thebaseband back end 226 may be incorporated into a single package (e.g.,that encloses multiple integrated circuit dies) or integrated circuit,multiple packages or integrated circuits, or distributed across one ormore circuit boards. In these implementations, individual wires, circuitboard traces, or VLSI metal or polysilicon layers carry the interface206 signals between the RF processing circuitry and the basebandprocessing circuitry.

Furthermore, any of the circuitry underlying the functionality of the RFfront end 224 and the baseband back end 226 may be incorporated, withadditional functionality, into a single package or integrated circuit,multiple packages or integrated circuits, or distributed across one ormore circuit boards. As examples, the RF and baseband circuitry may beintegrated on a die with digital or analog processing circuitry forcellular telephony, PDA operation, or engine, instrument, or electronicscontrollers for automobiles. Thus, FIG. 2, and the examples given aboveare not limiting; rather, one of ordinary skill in the art willappreciate that the particular implementation, division offunctionality, and packaging of the circuitry that implements the RFprocessing, baseband processing, and interface 206 may vary widelydepending on the application at hand, engineering considerations, costconsiderations, and the like.

The interface 206 includes a message serial interface 208 and a dataserial interface 210. The message serial interface 208 provides forserial communication of general purpose messages bi-directionallybetween the RF section 202 and the baseband section 204. In contrast,the RF section 202 uses the data serial interface 210 to transmit SPSsignal samples to the baseband section 204.

As an initial matter, it is noted that in general, the interface 206signals shown in FIG. 2 are CMOS compatible. In particular, the inputs,for logic one, are above 0.7*Vcc V, and, for logic zero, are below0.3*Vcc V. Outputs, for logic one, are above Vcc-0.4 V, and, for logiczero, are below 0.4 V. The input/output pins generally operate in eitherthe 2.5 V or 3.3 V voltage ranges, depending on the desiredimplementation. The real time clock (RTC) input/output pins may operateat 1.5 V, although they may be designed to tolerate 3.3 V levels ifdesired. Any of the signals, however, may be adapted to differentvoltage ratings or specifications depending on the desiredimplementation.

The message serial interface 208, as shown in FIG. 2, includes themessage-in signal line (labeled MSG_DO/MI), a message-out signal line(labeled MSG_DI/MO), a message clock signal line (MSG_CLK/MK) and aslave-select signal line (labeled MSG_CEB/SS_N[0]). The labels on themessage signal lines indicate the direction of data flow from theperspective of the RF section 202/baseband section 204. For example, themessage-out signal line (MSG_DI/MO) carries message bits input to the RFsection 202 and output by the baseband section 204.

The data serial interface 210 includes the data clock signal line(labeled ACQCLK) and the data bit signal line (labeled SGNMAG). The dataserial interface 210 generally uses only a single data bit signal lineto communicate, serially, data bits to the baseband section 204 (asdiscussed below in greater detail with regard to FIG. 3). Thus, the dataserial interface 210 generally includes as few as two signal lines: onefor a data clock and one for data bits. The data serial interface 210 isthus a low complexity solution for a SPS signal sample interface betweenthe RF section 202 and the baseband section 204.

As shown in FIG. 2, the receiver section 200, on the RF processing side,also includes a real time clock ETC) oscillator (OSC) and monitorsection 212. A 32 KHz crystal (or other clock source) provides an inputclock 214 for the RTC OSC section 212. The RTC OSC section 212 generatesa clock output on the RTCLK/RIN signal line that the baseband section204 uses to keep, as examples, GPS time or UTC time. The clock outputis, for example, a 32,768 Hz 1.5 V CMOS output. The RTC OSC section 212continues to run during power down modes to help the baseband section204 maintain an accurate timebase.

However, monitoring circuitry (e.g., a rectifier coupled to the clockinput and followed by a comparator) in the RTC OSC section 212determines when the input clock 214 has consistently run (e.g., hasstopped for no more than 10-30 clock cycles). If the clock has stoppedfor too long, then the RF section 202 sets a bit (e.g., sets a flip/flopoutput or sets a bit in a multi-bit status register) to indicate thatthe clock output has not been consistent (and, in some cases, that thebaseband section 204 should search over the full range of the receivedSPS signal to determine the correct time).

The RF section 202 also accepts clocking input from either a crystaloscillator 216 or an external clock source 218 (e.g., a frequencyreference provided in a wireless device). The clocking inputs 216 and218 provide a clock source that a PLL divider chain in the RF section202 uses to generate the ACQCLK signal. The clocking inputs 216 and 218are collectively referred to below as the OSCCLK, while the PLL dividerchain clock is referred to as the PLLCLK. The PLLCLK is typically set togenerate a nominal frequency of 16 fo (where fo=1.023 MHz) on the dataclock ACQCLK derived from the OSCCLK (or an internal reference).

At power-up, the OSCCLK (generally in the range of 5-27 MHz) is presenton the ACQCLK output. A message (described below) commands the RFsection 202 to switch ACQCLK from OSCCLK to the PLLCLK and from thePLLCLK to the OSCCLK. The ACQCLK signal may be a 2.5/3.3 V CMOS outputwith a duty cycle between 45% and 55% (except when switching clocksources, in which case ACQCLK may have an extended low cycle).

A power control signal (labeled PWRUP/RFPWRUP) controls whether certainportions of the RF section 202 are powered-up. The power control signalmay be connected, for example, to a voltage regulator enable pin in theRF section 202. The RTC OSC section 212 is separately powered so that itcan continue to provide a clock to the baseband section 204. The powercontrol signal may be a 2.5/3.3 V CMOS signal. The baseband processingside includes an RTC logic section 220. The RTC logic section 220accepts the input clock generated by the RTC OSC and monitor section 212as an aide in determining the current time as well as SPS locationsolutions.

The RTC logic section 220 also outputs the reset signal GRFRST_N/RESET_N(asserted low). The reset signal may be used to reset the state ofcontrol registers in the RTC OSC section 212 and the RF section 202 atpower-on. For example, when GRFRST_N is asserted, the digital controlregisters on the RF processing side will be reset to their defaultstates. The default states of the control registers allow the OSCCLKcircuits to operate and allow the ACQCLK output to be driven by OCSCLK(when PWRUP) is asserted. When GRFRST_N is not asserted, then the RFsection 202 operates according to its internal logic states.

The message serial interface signals are 2.5/3.3V CMOS I/O signals. TheMSG_CLK/MK, MSG_DI/MO, and MSG_CEB/SS_N[0] signals are inputs to the RFsection 202. The MSG_DO/MI signal is an output from the RF section 202with tri-state control. When the MSG_CEB/SS_N[0] is logic high, theMSG_DO/MI output is high impedance and may be driven by other devicesthat are also connected to the message serial interface 208. Thus, theMSG_CEB/SS_N[0] output from the baseband section 204 operates as a slaveselection signal that allows the RF section 202 to drive data on theMSG_DO/MI signal line. When additional devices are attached to themessage serial interface 208, the baseband section 204 may provideadditional slave selection signal lines to determine which device isallowed to drive data on the MSG_DO/MI signal line.

The RF section 202 may also include one or more inputs for externalanalog sensors (not shown). Thus, a multi-channel analog to digital(A/D) converter in the RF section 202 may take measurements of analoginput signals and communicate the results to the baseband section 204.The analog inputs may include, but not be limited to, temperatureinputs, gyro turn rate inputs, wheel tick inputs, or a battery voltageinputs.

Table 1 summarizes the operating modes for the receiver section 200:

TABLE 1 Mode GRFRST_N PWRUP Operation Sleep 0 0 RF section voltageregulator disabled; RTC OSC section isolated from RF section. Start-up 01 RF section voltage regulator enabled; RTC OSC section isolated;registers reset; OSCCLK enabled; ACQCLK outputs OSCCLK. NA 1 0 Notallowed. Normal 1 1 RF section voltage regulator enabled; RTC OSCsection communicates with RF section; messages control RF sectionoperation.

Turning next to FIG. 3, that figure illustrates a timing diagram 300that shows the relationship between a data clock 302 and a data signal304. The data signal 304 provides SPS signal samples to the basebandsection 204. The SPS signal samples are derived from an SPS input signalreceived by an antenna connected to the RF section 202. The ACQCLKsignal line carries the data clock 302, while the SGNMAG SGN/MAG signalline carries the data signal 304. The data signal 304, which may be, forexample, a 2.5/3.3 V CMOS output, transmits both sign bit data 306 andmagnitude bit data 308 on the SGN/MAG signal line. In one embodiment,the data signal 304 provides sign and magnitude bit informationdetermined by an A/D converter in the RF section 202.

In other embodiments, additional bits of information or quantization maybe provided, in concert with a predetermined protocol or encodingtechnique applied to the data bits (e.g., a pseudorandom noise code) toallow the baseband section 204 to identify the data transmitted.Furthermore, the data signal 304 may transmit signal samples fordifferent radio chains handled by the RF section 202. For example, whenthe RF section 202 is processing SPS data, the data signal 304 may bearthe two bits per sample (sign and magnitude) data pairs noted above. Incontrast, when the RF section 202 is processing a different RF signal(e.g., a Bluetooth signal), the data signal 304 may instead transmitmore or less bits per sample (e.g., 4 or 6 bits) in accordance with theguidelines established for processing that RF signal. Similarly, thedata clock 302 may vary in frequency and duty cycle to meet theprocessing guideline for the RF signal that the RF section 202 iscurrently processing.

As shown in FIG. 3, the RF section 202 outputs the sign bit 306 when thedata clock 302 is high and outputs the magnitude bit 308 when the dataclock 302 is low. As shown in FIG. 3, the sign bit 306 is valid no lessthan T_(SETUP-F) before the falling edge 310 of the data clock 302.Similarly, the magnitude bit 308 is valid no less than T_(SETUP-R)before the rising edge 312 of the data clock 302.

The sign bit 306 remains valid no less than T_(HOLD-F) after the fallingedge 310 of the data clock 302. The magnitude bit 308 remains valid noless than T_(HOLD-R) after the rising edge 312 of the data clock 302.The setup and hold times may vary from implementation to implementation.As one example, the setup and hold times may be approximately 5-10 ns.

The message serial interface 208 may be implemented in a wide variety ofways. In one embodiment, the message serial interface 208 has thecharacteristics set forth below, although other implementations are alsopossible.

The message serial interface on the RF section 202 operates as a slavedevice to the baseband section 204 (or other master device that adheresto the characteristics set forth below). The input bits to the RFsection 202 (on the MSG_DI line) are shifted into a 32 bit shiftregister in the RF section 202 under control of the MSG_CLK. Data isreceived and transmitted with the most significant bit first. In oneimplementation, up to 32 bits are sent in one message block.Simultaneously, the MSG_DO output bits are shifted out of the other endof the same shift register. If output from the RF section 202 is notneeded, then the MSG_DO output need not be connected.

The MSG_CLK may, for example, operate at up to 20 MHz, while the messageserial interface inputs are above 0.7*VCC V for logic 1 and below0.3*VCC V for logic 0, and the outputs are above VCC-0.4 V for logic 1and below 0.4 V for logic 0.

The slave select signal line (MSG_CEB) is active low for serial datatransmission. The MSG_DI and MSG_CLK may therefore be ignored as long asMSG_CEB has been high for a pre-selected period of time (e.g., 5 ns).Data is sampled on the rising edge of MSG_CLK. In one implementation, atransition on MSG_DI or MSG_DO occurs at least 5 ns after the risingedge of MSG_CLK and stabilizes at least 5 ns before the next rising edgeof MSG_CLK. The data is shifted on the falling edge of MSG_CLK.Continuing the example, the MSG_CEB signal may be active (logic 0) atleast 10 ns before the rising edge of the first MSG_CLK and may remainactive (logic 0) at least 10 ns after the last falling edge of MSG_CLK.The time interval in both cases may be, for example, one half of oneclock cycle. The MSG_CEB signal may then be inactive (logic 1) for atleast 30 ns to ensure the data is latched.

If the MSG_CEB signal transitions high before all data in a messageblock have been sent, the data is discarded and not applied to RFsection 202 registers. Unused bits in a message block are set to zero.However, a fast write mode is provided to allow for a shortened, onebyte message. The fast write mode is assumed until more than 8 bits havebeen received. When more than 8 bits have been received, the RF section202 expects to receive a full 32 bits for a valid message.

The RF section 202 outputs data (on MSG_DO) to the baseband section 204in response to a message received from the baseband section 204 thatrequests the data. The baseband section 204 then sends a subsequentmessage to shift out the requested data in the RF section 202 shiftregister from the shift register. The subsequent message may be anindependent operational message or it may be a dummy message sent forthe sole purpose of shifting out the desired data.

FIG. 4 illustrates a timing diagram 400 that shows the relationshipbetween the slave select signal (MSG_CEB) 402, the message clock signal(MSG_CLK) 404, and the message data bit signals (MSG_DO and MSG_DI) 406.Data transmission starts when the slave select signal 402 fails. Thetransmitted data are latched when the slave select signal 402 rises.

As shown in FIG. 4, the message-out signal line (MSG_DI/MO) andmessage-in signal line (MSG_DO/MI) each carry a serial bit stream. Theserial bit stream on the message-out signal line represents a messageselected from a group of predefined RF section messages that aretransmitted from the baseband section 204 to the RF section 202.Similarly, the serial bit stream on the message-in signal linerepresents a message selected from a group of predefined basebandsection messages that are transmitted from the RF section 202 to thebaseband section 204.

The messages are not limited to any particular purpose or format. Asexplained in more detail below, the messages may include, but not belimited to, RF section power control messages, RF section test messages,clock status messages, analog measurement messages, channel conversioncount messages, and the like.

In one implementation, there are four types of message blocks defined.Data [1:0] (in a 32-bit or 8-bit sequence) are address bits that definethe four messages as shown in Table 2 below. Each message type is ableto support both a fast write mode and a fall write mode and sparecapacity has been defined for both modes.

TABLE 2 Message Blocks Data Message [1:0] Type Message Name 00 0 AGC(Fast Write) and Synthesizer 01 1 Power Control (Fast Write) andSynthesizer 10 2 Output Message Types 11 3 Input Message Type Expansion

The contents of each message are defined in detail in 3 through 8. Table3 shows AGC and synthesizer control messages, Table 4 shows powercontrol and synthesizer control messages, and Table 5 shows outputrequest types for a selected message type. Table 6 shows output messagetypes and Tables 7-8 show input message types, The columns define thecontents as follows. The first column, labeled Bits, represents themessage data bits, with bit 0 indicating the last bit transmitted. Thesecond column, labeled Field Name, identifies the name of the field inthe message. The third column, labeled Length, is the length of thefield. The forth column, labeled Default, indicates the contents of thedefault parameter in the RF section 202 when power is first applied. Thefifth column, labeled Contents, describes the allowed contents of thefield. The sixth column, labeled Function, indicates what the fieldaccomplishes. And, the seventh column, labeled_Pwr, indicates whichpower domain control bit, if any, is used to drive these field outputsto zero on the interface to the RF section 202.

Message type 2 provides for implementing output requests using a fieldthat specifies up to 32 types of output requests. Message type 3provides for expanding the input message types (or addresses) from 4 to36. References below to the “synthesizer” are references to the PLLsynthesizer clock generation circuitry in the RF section 202. The PLLsynthesizer is configurable, for example, by setting clock dividervalues to generate the PLLCLK from a number of different input referencefrequencies.

TABLE 3 Message Type 0: AGC and Synthesizer Control (Address [1:0] = 0)Bits Field Name Length Default Contents Function _Pwr 31:28 Spare0 [3:0]4 0 0 Spare 27:8  NUM [19:0] 20 TBD  0x00000-0xFFFFF Specifies thenumerator of Synth the fractional part of the loop divider in the PLLclock generation section of the RF section 202. 7:2 AGC [5:0] 6 00x00-0x3F Controls AGC gain in the Rx RF section 202 1:0 Address 2 0 0Defines message type [1:0]

TABLE 4 Message Type 1: Power Control and Synthesizer Control (Address[1:0] = 1) Bits Field Name Length Default Contents Function _Pwr 31:28Sparel [3:0] 4 0 0 Spare 27  InvertFePwr 1 0 0: Fe_Pwr = Rx_PwrPartition the 1: Fe_Pwr = ~Rx_Pwr reception chain in the RF section 202for testing purposes 26  WideBwFilter 1 1 0 = Narrow BW Select thefilter Rx 1 = Wide BW used in the RF section 202. 25:18 ND [7:0] 8 —0x00-0xFF Specifies the Synth integer part of a synthesizer loop dividerparameter in the PLL clock generation section 17:15 RDIV [2:0] 3 —0x0-0x7 Specifies a Synth synthesizer reference divider value in the PLLclock generation section 14:11 CP [3:0] 4 — — Specifies the PLLsynthesizer charge pump output and test modes 10  PD_POL 1 — 1 =positive, Specifies the PLL 0 = negative phase detector polarity 9 DvSel1 1 0 = Fractional Specifies the PLL 1 = Integer divider for PLLfeedback 8 SDO 1 1 0 = Third Order SD Chooses Sigma Synth 1 = FirstOrder SD Delta Order 7 Rx_Pwr 1 0 1 = on, 0 = off Controls front endpower for 2^(nd) low noise amplifier through A/D converter 6 AcqClk_Sel1 0 1 = PLL, 0 = Osc Controls glitch- free switch that selects OSCCLK orPLLCLK for ACQCLK 5 Synth_Pwr 1 0 1 = on, 0 = off Controls power tofractional N synthesizer 4 PLL_Pwr 1 0 1 = on, 0 = off Controls powerfor PLL and divider chain 3 LNA1_Pwr 1 0 1 = on, 0 = off Controls powerfor first (optional) LNA 2 Osc_Pwr 1 1 1 = on, 0 = off Controls powerfor oscillator, ACQCLK-select mux and ACQCLK driver 1:0 Address [1:0] 21 1 Defines message type

TABLE 5 Message Type 2: Output Request Types 0 to 31 (Address [1:0] = 2)Bits Field Name Length Default Contents Function 31:8  Spare2 [28:5] 240 0 Spare 7:3 Spare2 [4:0] or 5 0 0-31 Spare (Fast Write), if Out_Req =0 Out_Dat [4:0] Output data type, if Out_Req = 1 2 Out_Req 1 0 0 = dataWhen = 0, data follows 1 = output When = 1, output data to load follows1:0 Address [1:0] 2 2 2 Defines message type.

Output message types are shown in Table 6. Spare messages have beendefined for expansion or use in testing the RF section 202. Since thisdata is input to the message interface from the RF section 202, thesefields are given names denoting input, such as spareInA. When the datais shifted out, it is positioned in the output data stream using theindex values given. For example, spareInA [23:0] would be located in thefinal 24 bits shifted out in the 32 bit output field, so that eightleading zeros would be followed by spareInA [23] through spareInA [0]according to the convention of shifting out the most significant bitfirst.

Out_Dat [4:0]=4-8 specify 20-bit measurements taken by a dual slope A/Dconverter in the RF section 202. As noted above, the A/D converter mayhave multiple channels connected to one or more analog measurementdevices. As used below, Out_Dat [4:0]=9 specifies the valid clock bitmaintained by the RTC OSC section 212 and described above.

TABLE 6 Output Messages Defined Using Message Type 2 (Address [1:0] = 2and Out_Req = 1) Message Out_Dat [4:0] Bits Contents 0 31:24 0 23:0SpareInA [23:0] 1 31:24 0 23:0 SpareInB [23:0] 2 31:24 0 23:0 SpareInC[23:0] 3 31:24 0 23:0 SpareInD [23:0] 4 DS_ADC_CH_0 31:30 LAST_CH [1:0]29:20 Spare [9:0] 19:0 DATA0 [19:0] 5 DS_ADC_CH_1 31:30 LAST_CH [1:0]29:20 Spare [9:0] 19:0 DATA1 [19:0] 6 DS_ADC_CH_2 31:30 LAST_CH [1:0]29:20 Spare [9:0] 19:0 DATA2 [19:0] 7 DS_ADC_CH_3 31:30 LAST_CH [1:0]29:20 Spare [9:0] 19:0 DATA3 [19:0] 8 DS_ADC_CNT 31:30 LAST_CH [1:0]29:20 Spare [9:0] 19:0 COUNT [19:0] 9 RTC_STA 31:1 Spare [30:0]  0 0 =RTC Not Valid (default) 1 = RTC Valid 29 31:26 0 25:0 Power ControlMessage Register [24:0] 30 31:0 Message Input Shift Register 31 31:16 015:0 Chip Version [15:0]

TABLE 7 Message Type 3: Expanded Input Message Types (Address [1:0] = 3)Bits Field Name Length Default Contents Function 31:8  Spare3 [28:5] 240 0 Spare 7:3 Spare3 [4:0] 5 0 0-31 Spare (Fast Write), if or Addr_Exp =0 Address [6:2] Address expansion, if Addr_Exp = 1 2 Addr_Exp 1 0 0 =data When = 0, data follows 1 = address When = 1, address follows 1:0Address [1:0] 2 3 3 Defines message type.

Spare messages (useful for test or expansion purposes) are shown inTable 8. Because these data represent control bits output by the messageinterface to the RF section 202, the data fields have been named todenote outputs, for example, SpareOutA.

A test message has also been defined for the SGNMAG output signal line.When TestSignMag [8]=one, the test mode is entered. When the bit is azero, test mode is turned off. In test mode, the pattern specified inTestSignMag [7:0] is output, as long as ACQCLK is running, beginningwith TestSignMag [7] while ACQCLK is high.

TABLE 8 Input Messages using Message Type 3 (Address [1:0] = 3 andAddr_Exp = 1) Address [6:2] Msg Bits GRFRST_N Contents 0 31:8 0SpareOutA [23:0] 1 31:8 0 SpareOutB [23:0] 2 31:8 0 SpareOutC [23:0] 331:8 0 SpareOutD [23:0] 4 16:8 0 TestSignMag [8:0] 5 DS_ADC_PER 31:12 0PERIOD [19:0] 11 0 CLK_SEL 10 0 CLK_ENB  9:8 0 Spare [1:0] 6 DS_ADC_SH31:12 0 SHIFT [19:0] 11:8 0 Spare [3:0] 7 DS_ADC_PH 31:12 0 PH_ONE[19:0] 11:8 0 Spare [3:0] 8 DS_ADC_SEQ 31:12 0 CH_SEQ [23:0] 11:8 0Spare [3:0] 9 RTC_CTL 31:10 0 Spare [21:0]  9 0 1: Set RTC Status 0: Noaction (default)  8 0 1: Read RTC Status 0: No action (default) 10 SGNMAG_SIG 31:1 0 Spare [30:0]  0 0 0: SGNMAG (default) 1: OSCCLK

Address [6:2]=5-8 specify parameters for the dual slope A/D converter inthe RIP section 202. The DS_ADC_PER message sets the 20-bit conversionperiod, the duration of an entire A/D conversion cycle (PERIOD), selectsone of the input clocks (e.g., OSCCLK or PLLCLK) provided to the A/Dconverter (CLK_SEL), and enables or disables the clock (CLK_ENB). TheDS_ADC_SR message provides a 20-bit shift period (SHIFT) that the A/Dconverter control circuitry uses as a count down value before initiatingconversion in order to change the phase of the A/D conversion cyclesrelative to any given time base. The DS_ADC_PH specifies a 20-bit phaseone conversion period (e.g., the duration of the integration period) forthe dual slope A/D converter.

The DS_ADC_SEQ message specifies 24 bits that control the order in whichthe A/D converter performs a conversion on each of four input channels.More specifically, the 24 bits are partitioned into 12 pairs of bits;each pair specifies the next input channel to the analog multiplexerbefore the A/D converter. The pairs of bits thus control which channelis next digitized by the A/D converter and the four input channels maythereby be sampled at different rates.

Continuing with regard to Table 8, Address [6:2]=9 specifies that theclock status bit in the RTC OSC section 212 will be set to indicate agood clock, or (if bit 8 is a one) that the baseband section 204 isrequesting the value of the clock status bit to be output by the RFsection 202. Address [6:2]=10 controls (e.g., via a multiplexer) thesignal that the RF section 202 provides on the SGNMAG signal line. Thedefault is the sign bit and magnitude bit information, while thealternative is the OSCCLK signal.

Turning next to FIG. 5, that Figure shows a flow diagram 500 that showsa method for interfacing the RF section 202 and the baseband section204. In particular, with regard to the serial transmission of SPS signalsamples to the baseband section 204, the RF section 202 places a signbit 306 on the SGNMAG signal line (step 502), then provides a fallingedge 310 on the ACQCLK line (step 504). Subsequently, the RF section 202places a magnitude bit 308 on the SGNMAG signal line (step 506), thenprovides a rising edge 312 on the ACQCLK line (step 508). This sequencerepeats for each sign bit and magnitude bit sample pair transmitted tothe baseband section 204. SPS signal data is thereby seriallytransferred to the baseband section 204.

With regard to message transmission between the RF section 202 and thebaseband section 204, the master device (typically the baseband section204) determines whether it needs to send or receive data over themessage serial interface 208 (step 510). If so, the baseband section 204determines if the message is a fast write message (step 512). If themessage is a fast write message, then the baseband section 204 (if it istransmitting data) or the RF section 202 (if it is transmitting data)serially places 8 data bits on the appropriate serial message data line.Each data bit is shifted in by a message clock 404 transition for eachdata bit. (step 514). Otherwise, the baseband section 204 or the RFsection 202 serially places 32 data bits on the appropriate serialmessage line, with each data bit shift in by a message clock 404transition (step 516).

The slave select signal line may be used to transfer tiling between thebaseband section 204 and the RF section 202. In particular, theCOUNT[19:0] output (see Table 6, Out_Dat=8) represents the value of acounter present in the RF section 202 that reveals the sampling phase ofthe dual slope A/D converter in the RF section 202. The slave selectsignal line is connected to circuitry in the RF section 202 that latchesDSP timing. Thus, the COUNT value is the value in the counter at thetime the slave select signal causes the message that requests the COUNToutput to latch the COUNT value into the shift register fortransmission. In the baseband section 204, the slave select signallatches a counter (or another representation of time) when the slaveselected signal is de-asserted (which is also when the RF section 202latches COUNT).

The A/D sample timing may thereby be related to the baseband section 204timing. The SHIFT[19:0] input (see Table 8, Address=6) is used to shiftthe A/D timing to a desired offset from the baseband section 204 timing.As a result, the baseband section 204 may change the timing of the RPsection 202 circuitry without additional interface lines.

Thus, systems and methods consistent with the invention provideinterfaces (and methods of operating or providing interfaces) between anRF processing section 202 and a baseband processing section 204. Theinterface supports general purpose message transmission as well astransmission of SPS signal samples between the two processing sectionswithout adding undue complexity to the interface.

The foregoing description of the preferred embodiments of the inventionhas been presented for the purposes of illustration and description. Itis not intended to be exhaustive or to limit the invention to theprecise form disclosed. Many modifications and variations are possiblein light of the above teaching. It is intended that the scope of theinvention not be limited by this detailed description.

1. A method of interfacing a radio frequency (RF) section in a wirelessdevice with a baseband section in the wireless device, the methodcomprising: placing a first data bit of a data signal received by the RFsection on a single data bit signal line between the RF section and thebaseband section; providing a falling edge of a data clock on a dataclock signal line between the RF section and the baseband section;placing a second data bit of the data signal on the single data bitsignal line; providing a rising edge of the data clock on the data clocksignal line; serially communicating the first data bit and the seconddata bit to the baseband section on the single data bit signal line; andserially communicating the falling edge and the rising edge of the clocksignal to the baseband section on the data clock signal line; andrepeating the steps of the method for other pairs of data bits to becommunicated to the baseband section.
 2. The method of claim 1, whereinthe first data bit is a sign bit and the second data bit is a magnitudebit.
 3. The method of claim 1, wherein the wireless device is asatellite positioning system (SPS) receiver.
 4. The method of claim 3,wherein the first data bit, second data bit, and other pairs of databits are SPS signal samples derived from an SPS input signal received byan antenna connected to the RF section.
 5. The method of claim 1,further including the steps of: determining whether to send a messageover a message serial interface between the RF section and the basebandsection; if a message is to be sent, selecting the message to be sent;serially placing data bits of the selected message on a serial messagedata line; serially placing clock transitions equal in number to thenumber of data bits placed on the serial message data line; andtransmitting the selected message over the serial message data line. 6.The method of claim 5, wherein the step of determining whether to sendthe message is done by a master device.
 7. The method of claim 6,wherein the master device is the baseband section.
 8. The method ofclaim 6, wherein the step of selecting the message to be sent furtherincludes the step of determining whether to send the message in a fastwrite mode or a full write mode.
 9. The method of claim 8, wherein themessage in the fast write mode consists of 8 bits.
 10. The method ofclaim 8, wherein the message in the full write mode consists of 32 bits.11. The method of claim 5, wherein the message serial interface includesa message clock line, a message-out signal line from the basebandsection to the RF section, and a message-in signal line from the RFsection to the baseband section.
 12. The method of claim 11, furtherincluding the step of transmitting an output bit stream representing amessage selected from a predefined RF section message group on themessage-in signal line.
 13. The method of claim 12, wherein thepredefined RF section message group includes RF section power controlmessages, RF section test messages, and RF section programmable clocksynthesizer messages.
 14. The method of claim 13, wherein theprogrammable clock synthesizer messages include a reference dividervalue.
 15. The method of claim 14, wherein the reference divider valueis an integer divider value.
 16. The method of claim 14, wherein thereference divider value is a fractional divider value.
 17. The method ofclaim 13, wherein the predefined RF section message group furtherincludes clock output selection messages for selecting a message clockfor the message clock line.
 18. The method of claim 11, furtherincluding the step of transmitting an input bit stream representing amessage selected from a predefined baseband section message group on themessage-out signal line.
 19. The method of claim 18, wherein thepredefined baseband section message group includes clock statusmessages, analog measurement messages, and channel conversion countmessages.
 20. The method of claim 19, wherein the analog measurementmessages include an analog measurement message for at least one of aplurality of analog input channels.